Implicit framework references were disabled at the time we moved over to
the new SDK due to some remanants of project.json in our build. Those
have all been cleaned up now and hence moving us over to using implicit
framework references.

Not having this enabled meant the API surface we were targeting in our
projects was not actually what was available in the project target
framework. Instead it was the intersection of the target framework and
the set of NuGet packages we reference. This meant that code which
should work simply wasn't due to the API surface not being correct.

Many of our VB projects today rely on having an empty default namespace
and explicitly specifying the full namespace in source. In the new SDK /
dir props world this can only be done by explicitly marking the
namespace as empty in the project file. Can't do the centralized control
that we do today.

The test discovery is hurting our ability to load solutions quickly in
preview builds. Temporarily disabling discovery while this is being
fixed. Will re-enable once we have the fix.

This is at least temporarily using `dotnet vstest` to execute the tests.
That allows us to run the tests but can't do things like generate
compatible XML files that Jenkins can process.

The new structure of the tests does mean that our Linux / Mac jobs are
now broken though since we no longer have the deploy project.

This primarily moves us to the 2.2.0 version of xunit. In order to make
that transition though a number of other changes needed to happen as
well:

1. Needed to move our desktop target to 4.6.1. This should've been
required some time ago but we were essentially depending on bugs in the
SDK / NuGet.
1. Remove the DeployCoreClrTestRuntime project. This entire idea
depended on having the xunit.console.netcore package. This has since
been deleted and doesn't work with the 2.0 SDK.
1. Remove the deploy compiler tools project. Can just use dotnet exec
now and that's much more efficient.
1. Resolve a new ambiguity with KeyValuePair. A helper of ours now
exists in netcoreapp2.0.

I fully expect a number of Jenkins legs to fail with this change: build
correctness, coreclr and ubuntu. But I want to validate our other legs
and am still trackind down answers needed to fix the others.

Portable unit tests now build their desktop variants directly to the
UnitTests directory in a runnable state. This allwos tests to be run
directly and removes the need for the desktop deployment project.

In the new SDK we no longer have a need for ProjectGuid. This change
will:

- Remove ProjectGuid from project files
- Remove Name + Project items from ProjectReference entries
- Change BuildBoss to enforce both of these items

The warning B40057 used to be suppressed at a global level in PCL /
Desktop projects. The SDK does not suppress this warning and hence
converting to the new SDK caused this to show up.

Previously a number of developers fixed this problem individually. The
correct solution is to suppress it globally as was done previously.

This is an automated migration of our project files to the new SDK /
PackageReference.  It is done using the tool located here:

https://github.com/jaredpar/ConvertPackageRef